1. Field of the Invention
The present invention relates to flash butt welding, and particularly to apparatus for program control of flash butt welding.
Most efficiently the invention can be used in simultaneously welding several joints, as well as in welding articles having long seams to be formed, such as, for example, metal sheets measuring several meters in width and pipes of large diameters.
2. Prior Art
There is known a program control device for controlling a flash butt welding process (cf. USSR Author's Certificate No. 557,889) comprising welding current pick-ups switched into each welding circuit, and a welding program control unit having a power supply circuit and being connected through its output with a drive for moving workpieces being welded. This device further includes a peak signal detector having inputs connected to outputs of the welding current pick-ups and an output connected, through a parallel-connected proportional and real differentiating elements, to a comparator unit.
This prior art device operates as follows. A preset current magnitude from a pick-up, an actual current magnitude and a time derivative thereof are applied to the comparator unit. The amplified signal from the comparator unit is fed to the welding program control unit controlling the drive for moving the work-pieces being welded. It is to be noted that the speed of approach of the workpieces is proportional to the said signal.
Thus, the operation of the above device consists in detecting a maximal magnitude of the current density in one of the parallel circuits, and in controlling the welding process to maintain stability thereof based on the said maximal magnitude of the current density.
However, in the case of using the prior art device, a starting flashing allowance has to be increased. Moreover the welding time also has to be increased to compensate for an irregular preparation of abutting ends of the workpieces to be welded together, which in the end brings down the efficiency of the welding process. In addition non-uniform heating of individual joints being welded affects the quality of the resulting weld joints.